If you want more monitors than you’ve got DVI or VGA ports, your options include adding a video card, using a USB-based display, or this Matrox hack: a small box plugs into your computer’s monitor port, and two or three monitors plug into the box, no software drivers or additional hardware required.
If you want to send a video signal further than your monitor’s cable, your options include getting a longer cable (works up to about 50′) or get a different cable. From MAKE and Doug Burbridge: a sending VGA over Cat-5. This device promises to send DGA up to 600 feet. Or, send DVI 160 feet.